DESIGN FOR A BRAIN 5/8 



Such a mechanism may undergo two types of ' adaptation '. The 

 first occurred long ago and was the change from a species too 

 primitive to show such a reaction to a species which, by natural 

 selection, had developed the reaction as a characteristic inborn 

 feature. The second type of 4 adaptation ' occurs when a member 

 of the species, born with the mechanism, is subjected to cold and 

 changes from not-shivering to shivering. The first change 

 involved the development of the mechanism itself; the second 

 change occurs when the mechanism is stimulated into showing 

 its properties. 



In the learning process, the first stage occurs when the animal 

 4 learns ' : when it changes from an animal not having an adapted 

 mechanism to one which has such a mechanism. The second 

 stage occurs when the developed mechanism changes from in- 

 activity to activity. In this chapter we are concerned with the 

 characteristics of the developed mechanism. The processes which 

 led to its development are discussed in Chapter 9. 



5/8. We can now recognise that ' adaptive ' behaviour is equivalent 

 to the behaviour of a stable system, the region of the stability being 

 the region of the phase-space in which all the essential variables lie 

 within their normal limits. 



The view is not new (though it can now be stated with more 

 precision): 



4 Every phase of activity in a living being must be not 

 only a necessary sequence of some antecedent change in its 

 environment, but must be so adapted to this change as to 

 tend to its neutralisation, and so to the survival of the 

 organism. ... It must also apply to all the relations of 

 living beings. It must therefore be the guiding principle, 

 not only in physiology . . . but also in the other branches 

 of biology which treat of the relations of the living animal 

 to its environment and of the factors determining its survival 

 in the struggle for existence.' 



(Starling.) 



4 In an open system, such as our bodies represent, com- 

 pounded of unstable material and subjected continuously to 

 disturbing conditions, constancy is in itself evidence that 

 agencies are acting or ready to act, to maintain this constancy.' 



(Cannon.) 



4 Every material system can exist as an entity only so long 

 as its internal forces, attraction, cohesion, etc., balance the 



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